A couple of years ago I got a nasty surprise: my hard-earned JetBlue miles had "expired" due to "inactivity" in my account. It happens to thousands of people every year, usually with no warning.

Keeping track of the airlines' policies concerning the expiration of frequent flyer miles is a full time job. And while Delta Air Lines and JetBlue miles don't expire for now (that is, unless the member expires first), most airlines will wipe out your account if it's inactive for 12 to 18 months (Alaska Airlines miles may expire if there's no activity within 9 months of opening the account or two years with no activity, at their discretion). There are some exceptions: British Airways points expire after 36 months. Air Canada's miles expire after 7 years, whether or not there's account activity. Spirit Airlines' miles now expire after a paltry 3 months of inactivity. True, some airlines let you re-activate expired miles, but it will cost you.

But for most airlines, there's absolutely no excuse to let your miles expire, even if you don't fly or don't have an airline-branded credit card. You probably already do things that you could be earning miles for, as well as protecting the miles you have, but you're not aware of the possibilities. Do you make charitable donations? You could get bonus miles and extend your current miles for doing so. Planning on signing up for Netflix? Don't do it without going through your airline's website. About to have your taxes done by H&R Block? Do it through the US Airways website and you'll get 4 bonus miles for each dollar spent. Even a 99-cent iTunes purchase will earn you two Rapid Rewards points over at Southwest Airlines, extending your points for another 24 months.

Here are the top ways of adding activity to your account without flying and without using an airline credit card.

1. Dining for miles

This is one of the easiest ways. Although the restaurants participating in the airlines' dining for miles programs may not be Michelin 3-star establishments, there's probably at least one spot near you that you'd be happy eating at. In addition to generous miles per dollar awards, there are sign up bonuses. American and US Airways, for example offer 1000 miles after your first meal.

2. Shopping

Do you shop? Of course you do! But if you're not getting bonus miles, you're throwing good money away and failing to protect your frequent flyer account. Over 400 online merchants—Walmart, Drugstore.com, PETCO, JC Penney, Ann Taylor, Nike, and on and on--participate in the airlines' shopping mall programs. Even if you don't use an airline credit card, you'll get anywhere from 1 to 12 bonus miles for each dollar spent (sometimes more). And while it used to be that you had to shop online to get the miles, increasingly merchants such as Sunglass Hut are offering miles even for shopping in store or by phone. See links to the airlines' malls.

Most hotel chains participate. Stay in a hotel, give your frequent flyer number when you make the reservation or check in, get new miles, and protect the miles you have. (Some discounted hotel rates don't qualify for miles, so check before you book.)

5. Sending flowers

Valentine's Day looming? Mother's Day? Just because? You'll get 20 United miles per dollar at FTD Gifts and Flowers. Most other airlines participate.

6. Taking a cruise or vacation

Airlines offers big mileage bonuses on these when you book through their sites.

7. Investing

Transfer $100,000 into a Fidelity investment account and you'll get 50,000 United miles; $25,000 earns 15,000 miles. TDAmeritrade offers up to 25,000 miles for a new account. Other airlines offer similar perks.

8. Taking out a mortgage

Earn up to 50,000 United miles, for example, with a mortgage from Chase bank.

9. Signing up for Netflix

You'll get 1,500 American Aadvantage miles when you do. Other airlines participate. Planning on extending your Verizon or ATT Wireless contract for another two years? Do it through your airline's website and get bonus miles.

10. Donating to a charity

Give to the USO, Unicef, or cancer research (up to 10 miles per dollar donated) and you'll get American Aadvantage miles; you might help save lives, plus extend the life of your own miles.